56 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
TABLE 5.— The Foundation Coefficient (Distant Points). 









Rossi-ForEL SCALE. ABSOLUTE SCALE. r 
PLACE. OUNDATION 
(eesetice General Intensity. er General Intensity. ieee baie 
Salinas; 42 §-teeaeae IX IV+ 2,000 125 16 
San Jose eet Pe IX VETS. 2,000 300 i 
Santa Roses eee x VIII 2,500 1,200 2 
Ukiahitoegs. Sige ae VIII VII 1,200 250 5 
Willits ee eee eee IX VII 2,000 250 8 
Clear Lake" ==. = VIII VI 1,200 200 6 
Priest Valley .. . VII IV4 300 100 3 
Sacramento .. . VI} V4 200 125 2 
os Banosi-nae eee IX V4 200 125 16 
West San Joaquin Valley VITI + V4 1,600 125 12 





The intensities are given both in the Rossi-Forel scale and in the absolute scale of 
accelerations; the first column under each scale gives the apparent or felt intensity, 
and the second gives the general intensity or what seemingly would have been felt on 
solid rock if it had existed there. To determine the general intensity requires the exercise 
of some judgment, guided of course by the intensity map, No. 23; this quantity there- 
fore is subject to considerable error. The same is true of the values in the absolute 
scale; we have used Professor Omori’s estimates of the absolute values of the Rossi- 
Forel scale for intensities of VII or more ' and Professor Holden’s estimates for the lower 
intensities. The difficulties of obtaining the correct intensities, apparent and general, 
according to the Rossi-Forel scale, and the further difficulty of translating into the ab- 
solute scale, on account of the larger difference between the successive degrees of higher 
numbers of the former scale, make the values obtained only approximate; therefore it 
must be recognized that the foundation coefficients are far from accurate. 
The regions about Sacramento, Santa Rosa, and Priest Valley seem to have had 
their intensities increased least of all the alluvial basins. The great destruction of 
Santa Rosa suggested a special disturbance in that region, but this seems entirely un- 
necessary in view of its low coefficient in the table. The Salinas and San Joaquin 
Valleys have exceptionally high coefficients. The value at Salinas is probably ac- 
counted for by the extremely loose character of the alluvium in the flood-plain of the 
river and its nearness to the fault; but the low value at Sacramento suggests that a 
similar explanation may not be satisfactory for Los Banos and the San Joaquin Valley; 
and the high intensity the whole length of this valley has suggested an auxiliary fault in 
the region. The fact that the greatest northeastern extension of the lower isoseismals is 
not opposite the center of the known fault, but almost opposite its southern end; and the 
extension of the same isoseismals to the southeast, where they are more nearly symmet-. 
tical with respect to the San Joaquin Valley than with respect to the known fault, sup- 
port the view of an auxiliary fault in or near this valley. On the other hand, it is quite 
possible that the intensity in the valley has been overestimated, and that the alluvial 
character of the ground may account for the intensity that actually existed there. I am 
inclined to think an auxiliary crack the best explanation of the high intensity in the San 
Joaquin Valley; but the evidence for it is by no means satisfactory. (See further, vol. 1, 
pp. 344, 345.) 
The great differences in the coefficients found for the different alluvial basins are much 
too great to be accounted for by inaccuracies in their determinations; we must conclude 
that there are differences in the character and in the depth of the alluvium in different 
basins, and probably even in different parts of the same basin, which are important 
factors in the values of the coefficients. 

1 Publications of the Earthquake Investigation Commission in Foreign Languages, No. 4. 
? Dutton’s Earthquakes, p. 128. 
